The present invention relates generally to axial flow combine harvesters and, more particularly, to an improved rasp bar configuration for the threshing rotors.
It has been found that straight rasp bars positioned approximately 180 degrees apart along the circumference of the threshing rotor encounter rotor torque variations as the rasp bars pass over the crop in the rotor concave area. When large amounts of crop material is fed into the rotors, particularly under conditions where the crop material is green, wet or includes tough straw, an objectionable rumbling noise is produced. It is felt that this rumble occurs when the rasp bars overrun the crop mat in the rotor chamber causing the crop material to be alternately compressed and released.
As the circumferentially opposed rasp bars alternately pass over the concave area and compress the crop in the threshing process, the torque required to power the rotors fluctuates, causing a great exertion of force on the concave, concave supports and drive elements. These conditions induce fatigue stresses into the rotor gearboxes and couplings, as well as in the concaves and supports. It has also been noted that there is a tendency of somewhat wet or green straw and/or weeds to roll into a rope, entrapping grain and resulting in additional grain losses as the entrapped grain becomes discharged from the machine.